1. Technical Field
Embodiments relate to solder for bonding microelectronic devices. In particular, an embodiment relates to a solder paste that includes in situ alloying components that form an alloy during assembly reflow.
2. Description of Related Art
Where a microelectronic device is sensitive to conventional oven reflow temperatures, which are about 200° to 220° C., reflow of electrical bumps needs to occur at temperatures less than about 125° C. The operating temperature range of a microelectronic device, however, can be in the range from about 50° to about 80° C. Such a device requires the solder to have a higher liquidus temperature to reduce thermally accelerated solder joint reliability failure modes such as creep and fatigue that can occur at the ordinary operating temperature range of the device. Multiple solder bump reflows and burn-in testing can make solder joint failure and device failure more likely.
One approach to the temperature sensitivity of solders is to use solder alloys such as tin-antimony, tin-lead, and tin-indium. These solders, however, are also susceptible to thermally accelerated solder joint reliability failures such as creep and fatigue. One board mounting process with conventional solders requires at least two solder bump reflows. They include a ball attach first reflow and a board attach second reflow.